1. Field of the Invention
This invention relates to a dispenser for a controlled discharge of polymerizable compositions consisting of a powder and a liquid in the making of dental plates for prosthodontic and orthodontic purposes in a process in which the liquid is applied to a layer of the powder on a model and the powder and liquid are polymerized on said model.
2. Description of the Prior Art
It is known that plates for prosthodontic or orthodontic purposes can be made in that spray nozzles connected to bottles containing polymerizable compositions consisting of a powder and a liquid are held over the model and manual pressure is applied to each bottle so that powder is sprinkled and liquid is sprayed out of the nozzle that is held over the model. It is also known to use a pump for applying the liquid to the model on which a powder layer has been formed.
In other known dispensers the powder and the liquid are applied by means of a hand-held gun having two outlets. In such a dispenser the powder and liquid to be applied to the model are respectively fed by means of a feed screw and a pump. In said dispensers the nozzles for discharging the powder and the liquid must be sufficiently spaced apart because the liquid must not contact the powder in the jet when the liquid and powder are discharged at the same time. During a polymerization, the powder will absorb the liquid and will thus be wetted by the liquid over a distance of 6 to 10 millimeters, depending on the rate at which liquid is discharged. In such a hand-held gun, a simultaneous discharge of powder and liquid may result in a polymerization in the powder in the nozzle so that the latter will be clogged. Owing to the large spacing required between the nozzles, the powder and liquid can be simultaneously applied to the model only on a relatively small area so that the tooth fissures of the plaster model cannot be exactly filled. Besides, the feeding means of said known dispensers do not permit of a fine adjustment of the discharge rates.
In the manufacture of plates for prosthodontic or orthodontic purposes the powder is sprinkled onto the plaster model to form a strip-shaped layer and the liquid is then applied to said layer. In dependence on the velocity at which the liquid impinges on the powder, the latter will be formed with craterlike or furrowlike elevations and depressions so that the surface of the plate that is formed must subsequently be smoothened by milling polishing at high costs in order to minimize the annoyance of the patient by the plate. It must be borne in mind that the tongue is the most sensitive part in the mouth.
Noxious vapors are evolved during the polymerization and as the liquid impinges on the powder. For this reason the operation can be carried out only by a person wearing a gas mask or if the vapors are sucked off by an exhaust fan. In the known methods in which the spraying bottle, the pumping apparatus or the gun are held by one hand and the model is held by the other hand, the suction pipe must be widely spaced apart from the plaster model and from the spraying apparatus because the orientation of the model must be varied during the operation. Besides, an adequate vacuum cannot be applied because otherwise the powder may be sucked away from the model or the powder or liquid may be sucked out of the jet into the suction device. It must be borne in mind that without an adequate exhausting of the monomer vapors the latter will be dispersed throughout the laboratory, which in most cases is included in the dentist's office, so that there will also be an annoyance of the people working in the office and of the patients.